(2012/02/06 12:40), Xiao Guangrong wrote:
On 02/05/2012 07:42 PM, Takuya Yoshikawa wrote:From: Takuya Yoshikawa<yoshikawa.takuya@xxxxxxxxxxxxx> This patch fixes a race introduced by: commit 95d4c16ce78cb6b7549a09159c409d52ddd18dae KVM: Optimize dirty logging by rmap_write_protect() During protecting pages for dirty logging, other threads may also try to protect a page in mmu_sync_children() or kvm_mmu_get_page(). In such a case, because get_dirty_log releases mmu_lock before flushing TLB's, the following race condition can happen: A (get_dirty_log) B (another thread) lock(mmu_lock) clear pte.w unlock(mmu_lock) lock(mmu_lock) pte.w is already cleared unlock(mmu_lock) skip TLB flush return ... TLB flush Though thread B assumes the page has already been protected when it returns, the remaining TLB entry will break that assumption. This patch fixes this problem by making get_dirty_log hold the mmu_lock until it flushes the TLB's.I do not think this is a problem since the dirty page is logged when the writeable spte is being set, and in the end of get_dirty_log, all TLBs are always flushed.
The victim is not GET_DIRTY_LOG but thread B; it needs to assure the page is protected before returning. Thanks, Takuya -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
